JPS61158283A - Time base corrector - Google Patents

Abstract

PURPOSE:To prevent phase detection errors of reproduction video signal due to a drop-out by detecting the drop-out of the reproduction video signal and inhibiting the pulse signal showing the time base fluctuation of the reproduction signal for a period corresponding to the detected drop-out. CONSTITUTION:The output of an RF amplifier 2 is supplied to a drop-out detecting circuit 13 for detection of a drop-out period. For this drop-out period, a composite synchronizing signal obtained by supplying the video signal obtained via an FM modulator 3 to a synchronizing separator 15 is supplied to a gate circuit 16. Then the synchronizing signal component included within the drop-out period is extracted at the output side of the circuit 16. The output of the circuit 16 is supplied to a mono-multivibrator 18 which is triggered by the rear edge of the output signal of a mono-multivibrator 17. Thus a time-delayed pulse is produced to inhibit the sampling pulse produced from the output signal of a variable delay circuit 4 and supplied to a phase comparator 10 through a gate circuit 19.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a time axis correction device commonly used to remove time axis fluctuations in a video signal reproduced from a recording medium such as a video disk.

[Conventional technology]

An example of a conventional time base correction device using a CCD delay circuit as a variable delay circuit will be described with reference to FIGS. 3 and 4.

In FIG. 3, a playback signal (FIG. 4A) optically read from a video disc is supplied to an input terminal indicated by 21. This reproduction signal is transmitted to the FM via the RF amplifier 22.
? It is supplied to the ijmm unit 23.

At the output terminal of the FM demodulator 23, a reproduced video signal (FIG. 4B) containing jitter corresponding to time axis fluctuation appears. When this reproduced video signal passes through the COD delay circuit 24, time axis fluctuations are removed and a stable video signal (FIG. 4C) is taken out to the output terminal 25.

The CCD delay circuit 24 includes a VCO (voltage controlled optical oscillator)
Clock pulses from 26 are provided.

The oscillation frequency of this VCO 26 is controlled so as to remove the time axis fluctuation. A composite synchronization signal (fourth
Figure D) is the separated force, ro. This composite synchronization signal is supplied to a monomulti (abbreviation for monostable multiby-break) 28,
The 172-cycle horizontal synchronization signal is removed. mono multi 2
A horizontal synchronizing signal (FIG. 4E) generated at the output of 8 is supplied to monomulti 29. The monomulti 29 uses a sampling pulse (Fig. 4F) that rises from the leading edge of the horizontal synchronization signal.
) to form. This sampling pulse is supplied to one input terminal of the phase comparison circuit 30.

The other input terminal of this phase comparator circuit 30 is supplied with a trapezoidal wave from a trapezoidal wave generating circuit 31 .

The trapezoidal wave generating circuit 31 generates a trapezoidal wave (FIG. 4H) synchronized with the reference horizontal synchronizing signal (FIG. 4G) from the terminal 32. The phase comparator circuit 30 has a configuration of a sampling and holding circuit, and samples the slope portion of the trapezoidal wave using a sampling pulse.

The error voltage (fourth
FIG. 1) has a level corresponding to the phase difference between the sampling pulse and the reference horizontal synchronizing signal. Phase comparison circuit 3
The oscillation frequency of the CO 26 is controlled by the error voltage from 0, and the delay time of the CCD delay circuit 24 is controlled. As a result, time axis fluctuations in the reproduced video signal are removed.

[Problem that the invention seeks to solve]

The above-mentioned time axis correction device has the following drawbacks. In FIG. 4A, if dropouts as shown at 41 and 42 occur, the dropouts shown in FIG. B and Figure 4C, 43
Noises corresponding to the dropouts 41 and 42, as shown by 44 and 44, appear. The problem is noise 43 at the leading edge of the horizontal synchronization signal.

That is, this noise 43 is also generated at the output of the synchronous separation circuit 27, and the monomulti 29 is triggered by the noise, thereby generating the sampling pulse 45 shown in FIG. 4F. This sampling pulse 45 is shifted to a position earlier than the regular sampling pulse 46 shown by the broken line in FIG. 4F.

Therefore, the level of the error voltage detected by this sampling pulse 45 has dropped rapidly, as shown in FIG. 4. Therefore, image distortion and color unevenness occur on the screen, resulting in an unsightly screen. Particularly in video discs, narrow dropouts occur frequently, and this problem frequently occurs.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a time axis correction device that prevents errors in detecting the phase of a reproduced video signal due to dropouts.

Means for Solving Problem c] This invention demodulates a reproduced signal from a recording medium to obtain a reproduced video signal, supplies this reproduced video signal to a variable delay circuit 4, and outputs a video signal from the variable delay circuit 4. Generates a pulse signal representing the time axis variation of the reproduced signal based on the horizontal synchronization signal or burst signal separated from the signal, compares this pulse signal with a reference signal, and removes the time axis variation using this comparison output The present invention relates to a time axis correction device that controls the amount of delay of the variable delay circuit 4.

The present invention provides a processing output 41. of the reproduced video signal.
Dropout detection circuit 13 detects 4-2 and generates a detection pulse with a pulse width corresponding to the dropout period.
, a gate circuit 16 for extracting the detection pulse of the horizontal synchronization signal or burst signal section separated from the reproduced video signal; means 17 and 18 for delaying the detection pulse obtained at the output of the gate circuit 16 for a predetermined time; This is a time axis correction device comprising a gate circuit 19 which inhibits a pulse signal representing a time axis variation of a reproduced signal using a delayed detection pulse.

[Effect]

The dropout detection circuit 13 detects a dropout l- period from the reproduced signal at the input end of the variable delay circuit 4. The synchronization signal is separated from the video signal obtained by demodulating the reproduced signal, and the synchronization signal portion included within the detected dropout period is taken out as the output of the gate circuit 16. The pulse signal obtained by delaying the output of the gate circuit 16 prevents the sampling pulse formed from the output signal of the variable delay circuit 4 from being supplied to the phase comparator circuit by one gate circuit. Therefore, detection of time axis fluctuations using a sampling pulse with an incorrect phase due to the effect of dropout is prevented.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, a playback signal (FIG. 2A) optically read from a video disc is supplied to an input terminal indicated by 1. This reproduced signal is supplied to an FM demodulator 3 via an RF amplifier 2. The output terminal of this FM demodulator 3 receives a reproduced video signal (see Fig. 2D
) appears.

When this reproduced video signal passes through the CCD delay circuit 4, time axis fluctuations are removed, resulting in a stable video signal (Fig. 2).
is taken out to the output terminal 5.

CCI) delay circuit 4 includes a VCO (voltage controlled oscillator)
A clock pulse from 6 is provided. The oscillation frequency of this VCO 6 is controlled so as to remove time axis fluctuations. A composite synchronization signal (J in FIG. 2) is separated from the video signal taken out at the output terminal 5 by a synchronization separation circuit 7. This composite synchronization signal is supplied to a monomulti (abbreviation for m-stable multi-by-break) 8, and the 172-cycle horizontal synchronization signal is removed. A horizontal synchronizing signal (K in FIG. 2) generated at the output of the monomulti 8 is supplied to the monomulti 9.

The monomulti 9 uses a sampling pulse (see Fig. 2, 1,
) to form. This sampling pulse indicates the phase of the output video signal of the CCr delay circuit 4. This sampling pulse is supplied to one input terminal of the phase comparison circuit 10 via an AND gate 19.

A trapezoidal wave from a trapezoidal wave generating circuit 11 is supplied to the other input terminal of the phase comparison circuit 10.

The trapezoidal wave generating circuit 11 generates a trapezoidal wave (N in FIG. 2) synchronized with a reference horizontal synchronizing signal (M in FIG. 2) from the terminal 12. The phase comparison circuit 10 has a configuration of a sampling and holding circuit, and samples the slope portion of the trapezoidal wave using a sampling pulse.

The error voltage (second
Figure O) has a level corresponding to the phase difference between the sampling pulse and the reference horizontal synchronization signal. Phase comparison circuit 1
The oscillation frequency of the VCO 6 is controlled by the error voltage from 0, and the delay time of the CCD delay circuit 4 is controlled. As a result, time axis fluctuations in the reproduced video signal are removed.

In this embodiment, a dropout detection circuit 13 is provided to which the output of the RF amplifier 2 is supplied. The output signal of the dropout detection circuit 13 is supplied to the OFF delay circuit 14. The drop alert detection circuit 13 is shown in FIG.
As shown in FIG. 2B, when a playback signal from a video disc includes dropouts 41 and 42, a detection pulse that becomes high level corresponding to the dropout section is generated as shown in FIG. 2B.

The OF'F delay circuit 14 is a dropout detection circuit 13.
It has a monomulti configuration that is triggered by the leading edge of the output signal. The output signal of this OFF delay circuit 14 is as shown in FIG. 2C. The OFF delay circuit 14 is provided to compensate for the delay of the noise 43.44 (see the second diagram) caused by the dross noise filter 41.41 due to the filter of the FM demodulator 3, etc.

A sync separation circuit 15 is provided to which a video signal (FIG. 2D) from the FM demodulator 3 is supplied, and a composite sync signal shown in FIG. 2E is taken out by the sync separation circuit 15. OF
The output signal of the F delay circuit 14 and the output signal of the synchronous separation circuit 15 are supplied to an AND gate 16. AND gate 1
From No. 6, only the portion near the leading edge of the synchronization signal in the dropout section is extracted.

The leading edge of the output signal (FIG. 2F) of the ANr) gate 16 triggers the monomulti 17.

Therefore, the output signal shown in FIG. 2G is generated from the monomulti 17. A monomulti 18 is provided which is triggered by the trailing edge of the output signal of the monomulti 17, from which the output signal shown in FIG. 2H is generated.

The output signal of the monomulti 18 is inverted by an inverter 20 and supplied to an AND gate 19.

The monomulti 17 and the monomulti 18 have delay times corresponding to the variable range of the delay time of the CCD delay circuit 4. The delay time of the CCD delay circuit 4 changes depending on the time axis variation to be corrected. Therefore, the phase of the sampling pulse indicating the phase of the output signal of the CCD delay circuit 4 can vary within the range indicated by T in FIG.

Monomulti 17 and monomulti 18 generate pulse signals that inhibit sampling pulses included within this range T.

Since the pulse from the inverter 20 is supplied to the AND gate 19, the sampling pulse generated at the output of the AND gate 19 is as shown in the second diagram. As is clear from this second diagram, sampling pulses affected by noise caused by the dropper 1~ are prohibited from being supplied to the phase comparator circuit 10. Therefore, the error voltage from phase comparison circuit 10 is held at the previous value.

Alternatively, the delay time of the OFF delay circuit 14 may be increased to suppress not only the dropout within the sync signal section but also the noise due to the dropout immediately before the leading edge of the sync signal. Further, the present invention can also be applied to a time axis correction device configured to detect a time axis variation from a burst signal.

〔Effect of the invention〕

According to the present invention, it is possible to prevent erroneous detection of time axis fluctuations in a reproduced video signal from a recording medium and deterioration of reproduced image quality due to dropout.

In addition, in this invention, since only the drop error that affects the detection of time axis fluctuations is considered as a problem, it is possible to prevent the detection of time axis fluctuations from being prohibited more than necessary or the circuit configuration from becoming complicated. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of this invention, FIG. 2 is a waveform diagram of each part used to explain the operation of an embodiment of this invention, and FIG. 3 is a block diagram of an embodiment of this invention.
The figure is a block diagram of a conventional time axis correction device, and FIG. 4 is a waveform diagram of each part used to explain the conventional time axis correction device. Explanation of main symbols in the drawings 1: Input terminal for reproduced video signal, 3: FM demodulator, 4:
COD delay circuit, 5: Output terminal, ? , 15: Sync separation circuit, 13: Nitrotube out detection circuit, 14: OFF delay circuit. Agent Patent Attorney Tadashi Sugiura <alO Tadashi Kuchida ○ Knee 4 )-):l(j ΣZ ○ --71511=

Claims (1)

[Claims] A playback signal from a recording medium is demodulated to obtain a playback video signal, the playback video signal is supplied to a variable delay circuit, and a horizontal synchronization signal or The variable delay is configured such that a pulse signal representing the time axis variation of the reproduced signal is generated based on the burst signal, this pulse signal is compared with a reference signal, and the time axis variation is removed by this comparison output. A time axis correction device for controlling the amount of delay in a circuit includes a dropout detection circuit that detects a dropout in the reproduced video signal and generates a detection pulse having a pulse width corresponding to the dropout period; a gate circuit for extracting the detection pulse in the section of the separated horizontal synchronizing signal or burst signal; means for delaying the detection pulse obtained at the output of the gate circuit for a predetermined period of time; A time axis correction device comprising: a gate circuit that prohibits a pulse signal representing a time axis variation;